The invention relates to thermoplastic molding compositions and more particularly to compositions containing polycarbonate.
The present invention relates to flame-resistant, mineral-reinforced polycarbonate compositions with a high modulus of elasticity, good thermal resistance, excellent processing behavior and with improved flow line strength.
EP-A 0 391 413 disclosed PC/ABS (polycarbonate and acrylonitrile/butadiene/styrene) compositions having a low linear coefficient of thermal expansion as well as a high impact strength and thermal stability. These contain 4 to 18 wt. % of an inorganic filler whose particles have a mean diameter/thickness ratio of 4 to 24. The inorganic filler is a lamellar material such as talcum and mica. The described molding compositions are not flame-resistant.
EP-A 0 754 531 describes, inter alia, PC/ABS compositions that are rendered flame-resistant with an oligophosphate derived from bisphenol A and that contain lamellar reinforcing agents. WO 00/46298 describes PC/ABS blends rendered flame-resistant with organophosporus compounds and that contain 0.1 to 5 parts by weight of talcum.
Molding compositions with lamellar fillers as described in the aforementioned documents generally have an unsatisfactory flow line strength.
Also known are PC/ABS molding compositions with fiber-like mineral fillers. U.S. Pat. No. 5,965,655 describes PC/ABS compositions containing wollastonite that are characterized in particular by improved surface characteristics and that have a so-called Class A surface. The preferably used wollastonites have a mean aspect ratio, i.e. a ratio of fiber length to fiber diameter, of up to 6. Molding compositions containing such wollastonites are as a rule insufficiently rigid, i.e. have too low a tensile/flexural modulus. The described molding compositions have not been rendered flame-resistant.
Also, the PC/ABS molding compositions of WO 98/51737, which are characterized by improved thermal stability, flowability, low temperature strength and dimensional stability, are not flame-resistant. The compositions disclosed there contain 1 to 15 parts by weight of a mineral filler such as talcum or wollastonite having a mean largest particle size of 0.1 to 30 xcexcm. In the case of fiber-like fillers such as wollastonite having a large aspect ratio, this limit is as a rule exceeded. The molding compositions of EP-A 1 038 920 contained a special melt polycarbonate, ABS and 5 to 200 parts by weight of a reinforcing filler have also not been rendered flame-resistant.
In EP-A 1 026 205 flame-resistant PC/ABS compositions with a low chlorine content are described, that contain 0.1 to 30 parts by weight of a silicate filler and that are characterized in particular by an outstanding resistance to hydrolysis. As filler there may be used talcum and mica, as well as wollastonite. The described molding compositions have an unsatisfactory flame resistance, thermal stability, too poor an ESC behavior, and in injection molding may lead to undesirable coatings on the tool due to bleeding of the flame-proofing additive (so-called juicing). This also applies to the PC/ABS molding compositions described in JP-A 11/199768, which contain only 0.5 to 5 wt. % of an inorganic filler and for this reason exhibit a rigidity that is inadequate for many applications.
The object of the present invention is accordingly to provide mineral-reinforced flame-resistant polycarbonate compositions that are characterized by an excellent flame resistance, especially also in the case of thin wall thicknesses, high rigidity, good thermal stability, toughness and an excellent processing behavior, i.e. by good flowability and extremely low tendency to form coatings on the tool surfaces during the injection molding processing, and by an outstanding ESC (environmental stress cracking) behavior as well as, in particular, a significantly improved flow line strength. Such molding compositions may be used to produce all types of molded parts, in particular thin-walled parts that have to satisfy stringent requirements as regards mechanical properties and flame-proofing.